The present proposal is the result of unexpected and exciting data obtained under the present grant GM 18051. Under this grant, we studied the dynamics of substrate binding, electron transfer, and product formation in the camphor hydroxylase system of Pseudomonas putida. The three components of the system are a flavoprotein, a 2Fe2S-protein, putidaredoxin, and cytochrome P450cam. Our approach consists in studying the reaction mechanism by using flash photolysis. The unexpected result turned up when we followed the kinetics of one particular reaction, carbon monoxide (CO) binding to P450, over the temperature range from 300K down to about 20K. In addition to the well- known biphasic reaction at room temperature, we discovered three more regions of differing kinetics behavior. Of particular interest is the one at the lowest temperature, between about 20K and 100K. This reaction extends over many orders of magnitude in time and does not follow a simple reaction law. It can be understood by assuming that it is governed not by a single activation energy, but by an energy spectrum. We have determined the energy spectrum for P450, and also for myoglobin. The present evidence indicates that this low-temperature reaction may be important for the biological behavior at room temperature. We propose to study first this low temperature reaction in more detail. In particular we will extend the measurements to other hemoproteins, and we will study substrates other than CO, for instance O2 and isonitriles. In this way we hope to be able to explain the details of the heme-substrate reaction mechanism. This approach may lead to a method to diagnose small changes in the protein structure that effect the active center. It is thus possible that a new method for diagnosing diseases in myoglobin, hemoglobin, and similar proteins, may be found.